UV erasable programmable read only memories (UVPROMs) are well known to those skilled in the art. These types of memories comprise distinct charge storage cells or sites and include a separate read/write line to each of the charge storage cells. In order to write data to the UVPROM, it is first bulk erased by exposing simultaneously all of the charge storage cells to UV light or radiation to leak off any charges stored by them. Then, data is written to selected charge storage cells by injecting charges in them with the corresponding read/write lines. These charges may then be detected with the read/write lines so as to read data from the charge storage cells. Since UVPROMs include separate read/write lines to the charge storage cells, the charge storage cells are not able to be spaced apart at nanometer level increments so that the overall size of the UVPROM could be reduced. However, a UVPROM type structure with charge storage cells at nanometer level increments could be used if a mechanism were developed that could (1) selectively and individually write data to each charge storage cell by leaking off a charge in the charge storage cell with UV light, and (2) electrically read data from each storage cell by detecting or sampling a charge in the charge storage cell without a read line to the charge storage cell.
Moreover, recently attempts have been made at providing data storage devices where data can be electrically or mechanically written to and electrically read from a storage medium at nanometer level increments. However, these data storage devices all suffer from significant problems.
For example, U.S. Pat. No. 5,317,533, describes a data storage device utilizing scanning tunneling microscope (STM) probes to read and write data to a storage medium by producing and measuring tunneling currents between the STM probes and the storage medium. Furthermore, U.S. Pat. No. 5,289,408 describes a similar data storage device with a piezoelectric positioning apparatus for positioning STM probes over the storage medium to read and write data to the storage medium. This positioning apparatus is bulky and impractical to use as a part of a data storage device in a computing system. Moreover, since positioning of the STM probes over the storage medium in the X and Y directions is limited to the range of movement of the X and Y piezoelectric translator elements of the positioning apparatus, the storage capacity of this data storage device is also limited by this range of movement. And, to increase this range of movement so that the storage capacity of the data storage device is increased, the size of the X and Y piezoelectric translator elements must also be increased. This unfortunately increases the overall size, read/write times, weight, and power requirements of the data storage device.
Furthermore, U.S. Pat. No. 5,038,322 describes still another data storage device that utilizes STM probes. In this storage device, the STM probes are used to deform a deformable storage medium to write data to it which is represented by the deformations. Then, by producing and measuring a tunneling current between the STM probes and the storage medium, the deformations can be identified so as to read from the storage medium the data that was written to it. However, the STM probes comprise a soft conductive material, such as conductive silicon, tungsten, aluminum, or gold which wears down after prolonged use in deforming the storage medium. Thus, the useful life of this type of data storage device is limited.